Led Driver - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

2.42 LED driver

Circuit 98: Constant current supply for LEDs
Setup information
Install the transistor, the diode and the two resistors as shown in Fig. 2.98. Then install the three jumper
wires. Check the placement on the board again and only then connect the battery.
Experiment
Although everything is wired correctly, nothing will happen when you connect the battery. Up to now you
still don't know the value of the LED. You can use any LED, whether red, yellow or green. Current will always
be high enough to deliver a bright LED light. Even if battery voltage drops, the LED will always shine with
the same brightness.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.98.
Components required:
1 x 2N3904 transis-
tor, 2 x 1N4148 silicon
diodes, 1 x LED (see
Experiment for value),
1 x 100 Ω resistor,
1 x 10 kΩ resistor,
1 x breadboard, 1 x 9V
battery with clip con-
nector
Fig. 2.98: Constant current
supply for LEDs
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